A combine is a machine that is used in grain farming to harvest a variety of crops from a field. Combines are typically self-propelled, but some are also towed and powered by tractors. As a combine moves through a field during a harvesting operation, the ripened crop is cut from the field by a header at the front of the combine. The crop is then transferred into threshing and separating assemblies within the combine, where grain is removed from the crop material. Crop material other than grain (MOG) is expelled from rear of the combine.
An impeller-type spreader is an assembly attached to the rear of the combine that is adapted to receive MOG expelled from the combine and evenly broadcast it over a wide area of ground behind the combine. The spreader typically comprises a right-side impeller and a left-side impeller that counter-rotate on parallel axes. Generally, distribution of MOG to the right-side of the combine is attributed to the right-side impeller, and similarly, distribution of MOG to the left-side of the combine is attributed to the left-side impeller. The overall width of MOG distribution by the spreader is largely dependent on the rotational speed of the impellers. The higher the rotational speed of the impellers, the wider the resulting broadcast width.
When MOG is broadcast by a spreader, it is desirable that the it cover only the region that the combine has just cut. External conditions, such as cross-winds and side-slopes can cause the MOG to be spread onto un-cut regions. In addition, crop conditions, such crop type and moisture content, can affect spreader broadcast width. Conversely, MOG from lighter and dryer crop may become spread well beyond the width of the cut portion. All of these conditions can result in uneven broadcast coverage of MOG over a harvested field, which is undesirable. Thus an effective means of maintaining a constant spreader broadcast width and location, irregardless of external or crop conditions, is desired.